The present invention relates to an automatic digital convergence correcting method and associated apparatus for use in a display that employs a cathode ray tube (CRT), and more particularly, to an automatic digital convergence correcting method and associated apparatus for processing a signal so as to produce a correction signal which automatically corrects misconvergence of a CRT.
In general, convergence in displays such as a CRT projector or projection television involves three electron beams (R, G and B) respectively emitted from three CRTs which are focused onto the same point on a shadow mask. Convergence must be corrected for two reasons: first, since the beam starting points are different due to the offset location of the three CRTs, the red, green and blue components of the displayed image are not correctly combined. As a result, the desired color may not be obtained. Second, since the distance from a deflection center point to a shadow mask screen or fluorescent screen differs depending on the screen shape, the adjacent fluorescent material cannot emit light, so that the proper color may not be achieved or the color may vary undesirably.
To achieve convergence, three pairs of U-shaped ferrite cores are wound with a horizontal convergence coil and a vertical convergence coil and are disposed in the neck of a cathode ray tube at 120.degree. intervals, so that the three electron beams can be converged onto the same point of a shadow mask screen (or fluorescent screen) for image display. In addition, permanent magnets are provided around convergence yokes which are disposed in the neck of a cathode ray tube at 120.degree. intervals. The permanent magnets which are inserted into the convergence yoke are employed for a static convergence, which primarily involves convergence at the center of the screen. A dynamic convergence where the environment of the screen is converged is realized by cyclically applying a predetermined parabolic current into a horizontal/vertical convergence coil.
However, even though correction time is short, the conventional analog convergence correcting method has a problem in that, when precise correction is necessary, the circuit therefor is overly complicated.
Accordingly, a digital convergence correcting method is introduced in order to improve the analog convergence correcting method. Although the digital processing of the digital convergence correcting method enables a precise convergence correction, precise correction is time consuming and complicated because a convergence correction is performed by manually moving the display. Additionally, a front-type projector needs to correct the convergence for every movement thereof.
U.S. Pat. No. 4,999,703 discloses an automatic image correcting method and apparatus therefor which employ a CRT for automatically controlling the convergence of a primary color image by sensing the test pattern location via an optical sensor for sensing the light reflected from a screen onto which a test pattern for each primary color image is irradiated.